by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

NBC News reports that Syria's military has loaded nerve-gas chemicals into bombs and is awaiting final orders from President Bashar Assad.

U.S. officials confirmed Wednesday to NBC that bombs had been filled with precursors for deadly sarin but that they had yet been loaded onto planes. On Tuesday, officials said there was no evidence the process had begun.

Fox News cites a senior U.S. official as saying the bombs must be used within 60 days or the chemical expires and must be destroyed.

At least three facilities produce Syria's chemical weapons, according to Global Security. They are located near Damascus, Hama, and Safira, near Aleppo, the heart of the opposition.

President Obama warned Assad of "consequences" if chemical weapons are used against rebellious Syrians.

"The world is watching," Obama said Monday during a Washington symposium on nuclear non-proliferation. "If you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable."

"We simply cannot allow the 21st century to be darkened by the worst weapons of the 20th century," he added.

In 1988, the late Iraqi dictator Saddam Hussein gassed Kurds with sarin, killing an estimated 5,000 men, women and children.

U.S. Secretary of State Hillary Clinton on Wednesday again warned Assad to not use such weapons against his people.

"Our concerns are that an increasingly desperate Assad regime might turn to chemical weapons, or might lose control of them to one of the many groups that are now operating within Syria," Clinton said in Brussels after NATO foreign ministers authorized the deployment of an anti-missile system in Turkey. "And so, as part of the absolute unity that we all have on this issue, we have sent an unmistakable message that this would cross a red line and those responsible would be held to account."

NATO Secretary-General Anders Fogh Rasmussen on Tuesday called Syria's stockpile of chemical weapons "a matter of great concern" that adds to the urgency of deploying the Patriot missiles in Turkey. He called any use of chemical weapons "completely unacceptable," saying it would result in "an immediate reaction."

Syria is one of eight nations that has not signed the Chemical Weapons Convention. The others are Angola, Egypt, Israel, Myanmar, North Korea, Somalia and South Sudan. U.N. Secretary-General Ban Ki Moon urged Syria last week to join the treaty.

" As a party to the 1925 Geneva Protocol, Syria is obligated by international law not to use chemical weapons under any circumstances," the statement said. "The Syrian Government must also ensure the safety and security of any stocks of chemical weapons it may possess."